1. Field of the Invention
The present invention relates to a coupling structure of a shaft body and a shaft joint.
2. Description of Related Art
A steering apparatus for a vehicle comprises: a steering shaft with one end connected to a steering wheel; a transmission shaft having, on one end thereof, a shaft joint connected to the other end of the steering shaft; and a pinion shaft coupled to the other end of the transmission shaft through another shaft joint and having a pinion meshing with the mid portion of a rack shaft which extends in the left and right direction of the vehicle.
The coupling structure of a shaft joint and a shaft body composed of a steering shaft or a pinion shaft is disclosed, for example, in Japanese Patent Application Laid-Open No. 2000-310232.
According to the coupling structure of Japanese Patent Application Laid-Open No. 2000-310232, an end of the shaft body is provided with a non-circular engagement portion having a pair of parallel flat faces on a part of circular circumferential surface, and a slip-off preventing groove with both ends facing the flat faces. The shaft joint has an engagement groove with which the engagement portion is engaged so that relative rotation is impossible, two concentric bores facing the engagement groove, and a nut member press-fitted into one of the bores. In addition, held on the outer periphery of the shaft joint is a plate body comprising: a regulating tongue for regulating the movement of the shaft body within the engagement groove; and a supported portion connected to the regulating tongue through a substantially U-shaped curved portion and supported by the press-fitting of the nut member. Bores corresponding to the above-mentioned respective bores are formed in the supported portion and a position facing the supported portion.
The shaft body and the shaft joint are coupled up by: inserting the engagement portion of the shaft body into the engagement groove of the shaft joint from the edge side in the depth direction of the engagement groove to engage the engagement portion with the engagement groove; inserting a bolt into the bores of the plate body and the shaft joint and the slip-off preventing groove; and tightening the bolt into the nut member, so that relative movement in the axial direction of the engagement groove and relative rotation are impossible. In this case, with the insertion of the engagement portion into the engagement groove, the regulating tongue of the plate body is deflected, and, after the engagement portion is engaged with the engagement groove, the regulating tongue is elastically restored, comes into contact with a side face of the engagement portion, and regulates the W movement of the engagement portion in a direction opposite to the insertion direction.
In the coupling structure constructed as described above, however, it is possible to insert the engagement portion of the shaft body into the engagement groove even when the shaft body is not engaged in the correct position of the engagement groove. Moreover, it is also possible to insert the bolt into the bores of the shaft joint and tighten the bolt even when the shaft body is not engaged in the correct position due to an insufficient amount of engagement. Therefore, there is a possibility that the shaft body and the shaft joint cannot be securely coupled. For example, even in a state in which the engagement amount is insufficient because the engagement portion of the shaft body is engaged at a position nearer to the longitudinal end of the engagement groove than the bores into which the bolt is inserted, it is possible to insert the bolt into the bores and tighten the bolt, however the shaft body is not securely coupled because the bolt is not inserted into the slip-off preventing groove of the shaft body. Accordingly, for example, when the above-mentioned coupling structure is adopted in a steering apparatus in which the space around the shaft joint is narrow and the process of coupling the shaft body and the shaft joint is performed in a state in which the coupling portion of the shaft body and the shaft joint cannot be seen directly, there is a possibility that the steering apparatus is mounted in the vehicle body in a state in which the shaft body is not engaged in the correct position due to the insufficient amount of engagement.